1. Field of the Invention
The present invention relates to multi-wavelength photoelectric measurement devices such as a confocal displacement meter, an interference displacement meter, and a color optical sensor capable of measuring the characteristic amount of a measurement object such as the thickness, distance, displacement, or color using multi-wavelength light such as white light.
2. Description of Related Art
A photoelectric measurement device emits visible light or infrared light from a light emitting unit and detects reflected light that has been reflected by the surface of a measurement object or transmitted light that has been transmitted through a measurement object by a light receiving unit. A measurement unit measures the characteristic amount of a measurement object such as the thickness, distance, displacement, or color according to a light intensity distribution of each wavelength in the light receiving unit (refer to U.S. Pat. No. 4,585,349, JP 2012-021856 A, JP 2010-121977 A, and JP 02-095222 A).
In conventional multi-wavelength photoelectric measurement devices, a white light source such as a halogen lamp or a xenon lamp, a white LED, or a super luminescent diode (SLD) is used as a light emitting source.
However, when a super luminescent diode (SLD) is used as a light emitting source, disadvantageously, desired measurement cannot be performed due to an insufficient wavelength width of emitted light depending on the measurement specification.
On the other hand, when a white light source such as a halogen lamp or a xenon lamp, or a white LED is used as a light emitting source, it is difficult to form an image having a small spot diameter due to a larger area of the light emitting unit. When light applied to a measurement object has a large spot diameter, light is also applied to an area other than a desired measurement object area, which may disadvantageously result in inappropriate measurement.
In particular, in a confocal displacement meter or an interference displacement meter, when light applied to a measurement object has a large spot diameter, not only the accuracy in the vertical direction with respect to the optical axis direction, but also the accuracy of measurement in the thickness and the displacement measured along the optical axis direction is deteriorated.
In order to solve such problems, the light emitting source may be provided with a diaphragm to reduce the spot diameter of light applied to a measurement object. However, white light sources such as a halogen lamp and a xenon lamp disadvantageously have a short life. Further, also when a white LED is used, since a white LED has a small light emission amount per unit area, the amount of light applied to a measurement object is small. Thus, disadvantageously, measureable objects are restricted, and the thickness and distance of a measurement object cannot be detected with high accuracy.